hazeltine



Feb. 19, 1929.

L. A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Original Filed July 5, 1923 4 Sheets-Sheet l L TTT 4- r,

INVENTOR MQ WQ ATTORNEYS Feb. 19, 1929. 1,702,402

L, A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Originl File ly 5, 1925 4 Sheets-Sheet 2 INVENTOR ATTORNEYS Feb. 19, 1929. 1,702,402

L. A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER gin Filed y 1925 4 Sheets-Sheet 3 INVENTOR 05 114.; Q BY 3M, Mai /m Mam.

ATTORNEYS Feb. 19, 1929.

L. A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Original Filed y 1923 4 Sheets-Sheet 4 INVENTOR [owls 14, fiazelzlhe {M ATTORNEYS lHlll II II II II II II llHI 30$ F1 8 3km E iwm Patented Feb. 19, 1929.

" UNETE stares Louis A. HAZEL-TINY), on

noizoimii; ew massif.

A FYI v-51in ""m' METHOD AND APPARATUS FOR BQWER.

' This invention relates to a method and apparatus for controlling the speed of alternating-current motors, particularly induction motors, operated through an electric valve converter. The various forms ofcircuit in \vhioh'such a valve converter may be employed and the structure and arrangement of the valves are discussed in'my patent application Serial'No. 649,536, filed July 5, 1923, of which this is'a division. I

A specific application of the valve conversion of this invention is the operation ot electric railways.- The most desirable form of power transmission over considerable disitanceslis by the'use of three-phase alternating current, since alternating current is most easily'transformed'in voltage. The most'desirable form'ot power for delivery 'to electric locomotives and cars is high' voltage direct-current, since'this' requires only a single contact conductor and avoids the interference witlrcommunication'lines that is ex- .perienced with single-phase alternating current. The most desirable type of motor would be the polyph'asesquirrel cage induction motor supplied with currents ofadjusting contacts and is most robust in construction, but requires variable frequency-tor ellicient speed control. These conflicting demands for the form of power can be reconciled by the use of valve converters, first converting three-phase alternating-current into high-voltage direct current at substations and then converting the direct current into variable-frequency polyphasc currenton the locomotive or cars.

The direct conversion between direct current and low-frequency alternating current requires :1 very largenumberot valves unless the voltage-ahsorbing and current-absorbing rolls and condensers are made large; moreover, the residual harmonics with a small number of valves would have'a frequency within the audible range and would therefore be likely to cause interference with telephone circuits. Further, the form of valve which forms part of this invention ismost suited to moderatelyhigh control frequency. For these reasons the conversions at the subled July syiezaseria no. 649,5

7 the conversion is} from glow frequency' to :moderately high" frequencyf iindthen from this high' frequency to direct current 3' on the electric locomotive for ear -the conversion is the reverse, from direct'fcurrentto moderately high frequency and fro'i'n this fhigli frequency to" low variable f frequency." These two 'conversionsbeing the samein form, but

' reverse in sense,'only t-he latter will be described'in detailm On-itheelectric locomotive all of-the main 'circu'it connections are"per- '-Inanent, i thus avoiding-heavycontacts and trode circiiits;athesefelectrodes b'eing i conprinciples disclosed ma'y be' einbodied -i n vaexn'ploymd for" various pur- I rrin'g to these 'dratvingg 2 Fig. shows the in'aiiii 'circuits' "of a preferred arrangement for employingelcct ric valves toconvert idirect-current power in 7 two steps? into variable-frequency alternating-curren't power for operating squirrelcage induction 'motors on an electric locomotive.-"-*-" Fig. 2 showsan alternative to Fig. '1.

Fig. 3 shows a modification of the directcurrent valve Str'ucture'of Fig. 1' or 2 to suit it tooperation atone-half the voltage.

et shows the control electrode circuits for the direct-current valve structure of the converter of Fig. 1; Fig. 4 shows the control electrodecircuits for the alternatingcurrent valvestructure ofthe converter of Fignfieshowsan elevation in section of the complete valve structure of Fig. 1; Fig. 5 shows a plan in sectio corresponding to Fig 5 v M in 'Fig. 6 is a detail in p'lan'and elevation of the valve structure of F igsi 5 and 5? I Fig. 7 shows a mechanical arrangement of ternat' I current valve system 303 or 313,, and is nally supplied over lines--304;to

squirrel-cage induction motors 305. The moderately high frequency '2 in the intermediate circuit should beconslderehly higher thanthelow frequency otIthe output circuit and will ordinarilybe of theorder ofa few luu dred or a few'thousaml cycles per second. -Th e voltages ofthe input ,and'output circuits may be of theordeeof a few thousand vqlts; ,The shunt condensea'sjQ and C, are :for the purpose of absorbing current harmonics. The series impedance atforded by the leakage reactance of the transformerabsorhs voltage harmonics and ,also serves to limit the current to a safe value when the motors erect standstillat very low ,frequency. The principles and details of l thesecireuitsareanoie iullydescribed in my .patent application previously referred to.

Fig. 3 shows ,how the direct-current valve converters of ;Figs; 1 and'2may be externally reconnected for operation 'at' half voltage; The, control forthe lower six valves must begreveised in phase, relative; to that'inl igs-l and-2. i

Fig. 4'* gives the control connections for the direct-current valve converter of Fig. 1; and Fig. 4" givesltheeontrol connections for the alternating-current valve converter of the same figure. The valve structures 301 and 303 are oi the magnetically guided, electrostatically controlled, thermionic type (a structure which is sliown in Figs. 5, 5" and (i) each valve having a separate grid represented in the conventional way. To give the rapid variationin grid p0tential required for highly eiticient valve operation, it is necessary to supply large momentary currents to the electrostatic capacities of the grids. .This is accomplished by suddenly charging the grids from the reservoir condense! C, or C"r through a control valve 401 or 403, the grid of which is controlled by a commutator, 411 or 413. In order that the same control valve may be used successively for all grids, a selector-commutator 421 or 4:23 is. employed.

Considering Fig. 4 in detail, the selector commutator 421 has four conducting seg- 'ments,- the two shorter of which are connected through slip-rings across the reservoir condenser C. whenthe control valve 401 the control valve 401.

.to the negative side'of C,.

closes. The two longer segments are connected through slip-rings to a rectifier 431 which maintains one positive, the other negative, with respect to the neutral point N of the direct-current valve converter. The. gridot the control-valve 401 is maintained negativenhy the negative small valve rectifier 441 except when the circuit is closed at the control commutator 411, when the grid is made positive by the positive small rectifier .451. .VVhen the grid is negative, of course "the control valve 40l is'opennnd when the g d zp si iv the wai e i .QIOSML. New

"consider. the v action with respect to the grids G and Gr beginning at the instant at the control commutator 41L The brush 404 at the right-of the selector commutator 42l-then connects the grids, Gr and Gr to the-positive ,sideeof condenser Crtlrrough 7 At the same time the brushjltil :at the left of the selector con-1 inutator connects the-grids G, and G (each through a biasing rectifier B, and BK.) This action took place suddenly when the control valve \vas closed and a relatively large-current ni'omentarilyvvas supplied by the reservoir condenser C, to charge the capacity of G, and (fr in series withthe capacity of G and G 'As the. commutators rotatein a.

counter-clockwise direction .the brush 4 64 spansover the insulation between the short segment and thelong segment marked At the same time the brush 461 connects the .other short segment momentarily to the long segment marked The control valve 401 being still closed, the reservoir condenser C is thus connected across rec-tifier 43-1 and is recharged. Shortly thereafter the contact on the control commutator 411 is broken and the control valve then opens, leaving the condenser C charged and on open circuit, readv for charging the next .set of grids G G G G' For nearly half a revolution the grids G and G, are directly connected through the segment to the positive terminal of the rectifier 431. and the grids G, and -G,, in series with B, and B, 'respe'ctirely, are directly connected through the segment to the negative terminal of 431. "V'heu th brushes 404 and 401 lea ve the long segments. the short segments are temporarily isolated becausethe control valve 401 is then open; the grids, being insulated, retain their charge and their potential for a short time. Control valve 401 is then closed (by having its grid made positive through another contact on 411) and a current is suddenly supplied by C to reverse the potentials of the grids.

As the system is six-phase there are SIX valve operations per cycle, requiring six shown in the fgurepThe control valve has justheen-closedby the closing of the circuit equally spaced contacts on the control commutator 411 and six equally spaced brushes on the selector commutator 421, the commutator-s being directly connected mechanically, as indicated by the dotted line. Of course the commutators may be constructed to operate at one-half or one-third of the speed by multiplying their contacts by two or three, respectively.

The potentials of the evenly numbered grids are required to be positive or negative with respect to the central main electrode, which forms the neutral point N' of the lircct-currcnt system; and this result is attained as described above by having N connected to the neutral point of therectifier 431. Onthe other hand, the potentials of the grids G,, G, and G; are required to be positive or negative with respective to the upper (positive) electrode; so these grids each require a positive bias with respect to the neutral point this bias being obtained through the rcctitiers B B and B Similarily the grids G Gr and G, are given a negative bias. by means of the rectifiers 13' B and 15',

The .rectifiers-431, 441, 451 and the Bs of Fig. 4, as well as 433, 443 and 453 of Fig. 4, have emissive cathodes and nonemissive anodes. The grids are constantly positive with respect to the anodes and alternately positive and negative with respect to the cathodes. All of these rectifiers are supposed to be supplied with voltages of rectan ular wave form such as may be obtained from one of the direct-current valves. The rectifiers 441, 451, 443, 453 and the Bs take. care of such small powers that they are best made single; while each part of the rectifiers 431 and 433 takes care of larger powers and is made double. The coils connected to the B rectifiers may be secondaries of the same transformers which supply other rectifiers. The control valve circuits C r, 401, 411, 44-1 and 451, and the bias. circuits B, B etc, should be arranged with low capacity to ground, as their potentials are required to change suddenly.

Considering Fig. '4 in detail. selector cont inutator 423 is arranged similarly to that of Fig. 4 except that the segment covers a little less than one-third of a circumference and (he segment covers a little less than two-thirds. The result is that the grids of the alternating-current valve system 303 are positive for one'third and negative for two-thirds of a cycle. As the neutral point N of the outputcircuit is connected to the neutral point of the rectifier 433, and as the potentials of the grids are required to be positive or negative with respect to the output electrodes (connected to the lines 304). there is inserted in series with each grid the secondary of a one-to-one transformer whose primary is connected between N and the corresponding output electrode. Thesetransformers cause the potentials of the grids to follow the potentials of the corresponding" output electrodes. Except for the differences just nating-current: control commutators :(413 and 423), or to a multiple of this speed in case the number of-segments of thesecommutators has been multiplied. In place of having the commutators operate at different speeds, they are preferably mechanically connected toloperate at the samejspeed, as by shaft308, and: motor 307 in Fig. '7, and one set of control brushes '(4($1466 or 471-476) is revolved ata speed corresponding to the desired output frequ nc H In case such a cascade valve iconverter were to be used to supply synchronous motors, the -output frequency .would .be the rotational frequency of these motors and would therefore directly determine" "their speed. This speed would be controlled by the speed of a pilot motor driving one set of control brushes. However, the squirrel-cage induction motors, which have been chosen as best suited for electriotractionpurposes, run at a speed less than synchronous speed by the slip. If the relative speed atthe control commutators is not allowed to vary with the load'on'the -motors, the latter' will have speed-torque characteristics similar to direct-current shunt motors with field control or armature voltage control; and speeds will be set approximately by the speed setting 0f the commutators, but will drop off slightly as load is added. On the other hand, if one set of control brushes, as 461466 (of course with the brush on 411), is driven positively by the rotor of the power induction motor, as motor 305 in Fig. 7, the speed being stepped up in a ratio equal to the number of pairs of poles (for the numbmof segments shown in the figure), and the other set of brushes instead of being sta tionery is allowed to revolve slowly, as by pilot motor 306 in Fig. 7, then the speedtorque characteristics of the power motor will be similar to those of a direct current series motor. The theory of this case is given in the following paragraphs:

For simplicity of discussion suppose the power motor to be bipolar and the commutators bipolar also (as in Figs-4 and 4",

Hit)

lit

where corrospwldlng segments are not repeated). Let us use the following notation:

n, motor speed, or the'speed, of the directcurrent control brushes, 4614(j6;

a motor slip speed;

n speed of alternating-current control brushes, 471476; n speed of control commutators 411, 421, 413, 423;

g E, motor voltage;

I, motor current;

r, resistance of main circuit;

D, motor torque;

It, k,ctc., constants Y 7.

Then the intermediate frequency is equal to (m n); the alternatin -current control frequency is (n w n and the-output'frequency is (n' n which is equel ito the synchronous speed.' Hencethe slipis That is, the motor slip is numerically'equal to the speed f the alternating-current control brushes, and is.'t'herefore capable of independent control, 'as by controlling the speed of motor 306 in' Fig. 7.

Now approximately the following relations obtain:

E= k 1i.+ m) +11; 1 stem; and 1) =15 14 Hence I. I I

-Wit-h m constant above, the two equations are of the sonic form, showing theinduction motor controlled as above to have characteristics like the direct-currentseries motor.

The mechanical arrangement for obtain- Finally 'ing the relations described above is shown lfl- Flg.'7. Brushes 461466, together with the brush on 411, are driven positively by the power motor "305; brushes Jib-476, together with the brush on 413, are driven by the pilot motor 306; and all commute-tors;

are mechanically connected by shaft 308 and driven by motor 307. The connections from the moving brushes and commutator segments to their respective stationary circuits may be inadein the usual way through slipindicated.

rings andlcuds placed hollow shafts, as

I 'lhef ordinary direct-current motor is properly described as asynchronously commutated synchronous motor, or simply a direct-current synchronous motor. duction motors controlled as. above are cor The inrespondingly described as non-synchronously commutated-induction m0tors,-.or simply direct-current. induction motors. A more elementary form of directcurrent induc- -tion motor would be one having an ordinary commutated-armatureand a field structure equipped with a squirrehcage winding instead ;of--:a direct-currentfield winding. If

tolywa L J r 1 The irect-currcn't valve system 301 and the'alternatingscurrent valvesystern 303 of Fig. 1 are shown combined in a single structure in Figs. 5 and 5", a detail being shown in Fig.6. Each valve system consists of a highly evacuated metal-vessel 501 and 503 containing main electrodes. 504 and control eleotnodestinrthe formof grids 505- All main electrodes -are electron-:emissive oi'er the portions 506 in 'the central-space between grid conductors, the heat developed by the losses maintaining the :proper temperature .for' emission. The valve systems are placed 'in' a constant magnetic field produced by the iron core 507 excitedbythe coils 508,509,

510, the: lin'es of magnetic fluir having the paths indicated by the dotted linesand serving to guide. the electrons so that they do not reach the grid conductors. The action is more fully discussed in my patent application previously referred to.

I claim: 4

1.=:A system for operating an alternatingcurrent motor from a source of directcurrent power, which comprises a cascade electrostatically controlled -'valve converter which converts the direct-current power first into high-frequency power and then into lo'\':-frequency polyphsse power for supply to the ureter. two positively connected. control commutator-s for said valve converter. a set of brushes for each of said commutators. and means for driving one set of ln'ushcs relatively to the other, the relative motion determining the'lfreqnency supplied to the motor.

2. A system for-attaining in an induction motor speed-torque characteristics like those of a direct-current series motor, which comprises a source of direct-current power, an electrostatically controlled valve converter which converts the direct-current power into polyphase power for supply to the motor,-

control means having an independent frequency, second control means having a frequency dependent on the motor speed, and means for making the output frequency of said valve converter equal to the sum of said frequencies.

3. A system for attaining in an induction motor speed-torque characteristics like those of a direct-current series motor, which comprises a source of direct-current power, a cascade electrostatically controlled valve converter which converts the direct-current power first into high-frequency power and then into low-frequency polyphase power for supply to the motor, two positively connected control commutators for said valve converter, a set of brushes for one of said commutators driven by the motor, and a set of brushes for the other of said commutators driven independently, whereby the frequency supplied to the motor is the sum of a frequency proportional to the speed of the motor and an independent frequency.

4. A system of motor speed control, which comprises a source of direct-current power, an alternating-current motor, a group of electrostatically controlled valves associated with said source of direct-current power, an intermediate circuit connectin said group of valves to a second group 0 electrostatically controlled valves, an output circuit-connecting said second group of valves to said motor, a commutator associated with the control electrodes of the first mentioned group of valves, a second commutator associated with the control electrodes of the second group of valves, brushes associated with each commutator, means moving said commutators relative to their respective brushes at speeds whose difference is adjustable and relatively small, said difference corresponding to the frequency of the current supplied to said motor which determines the speed thereof, and a reservoir condenser associated with each commutator, whereby the control electrodes are rapidly changed in potential.

5. A system of motor speed control having high efficiency, which comprises a source of power, an alternating-current motor, an electrostatically controlled valve converter interposed between said source of power and said motor, each valve of said converter having two electron-emissive main electrodes and a nonemissive control electrode, means for preventing electrons emitted by the main electrodes from reaching the control electrodes, a selector commutator associated with the control electrodes, a source of high positive and negative potential connected through said commutator to the control electrodes, whereby electron streams between the main electrodes are alternately established copiously and interrupted completely, a reservoir condenser connected through said commutator to the control electrodes, whereby the control electrodes are rapidly changed in potential, brushes associated with said commutator, means moving said commutator relative to said brushes at an adjustable speed, whereby the current supplied to the motor is adjusted in frequency and thence the speed is controlled, shunt capacity absorbing reactively differences between the input and output currents of the valve converter, and series inductance absorbing reactively differences between the input and output voltages of the valve converter,

whereby such current and voltage differences are not required to.be absorbed by the valves themselves. i

6; A system for attaining in an induction motor speed-torque characteristics like those of a direct-current series motor, which comprisesa source of direct-current power, a cascade electrostatically controlled valve converter which converts the direct-current power first into high-frequency power and then into low-frequency polyphase power for supply to the motor, two ositively connected control commutators or said valve converter, a set of brushes for each of said commutators, andmeans for driving one set of brushes relatively to the other at a speed which is determined as theusumof aspeed proportional to the motor speed and an independently controlled speed.

7. In an induction motor operated from a source of direct-current power, the method of attainin speed-torque characteristics like those of a ir'ect-current series motor, which comprises converting the direct-current power into polyphase alternating-current power whose frequency is the sum of two components, one component corresponding to and mechanically derived from the speed of the motor, and the other component corresponding to the desired slip of the motor and fixed Independently of the speed of the motor.

8. In an induction motor operated from a source of direct-current power, the method of attaining speed-torque characteristics like those of a direct-current series motor and of controlling the speed, which comprises converting the direct-current power into polyphase alternating-current power whose frequency is the sum of two components, one component corresponding to and mechani cally derived from the speed of the motor, and the other component corresponding to the desired slip of the motor and controlled by means rotating independently of the motor.

In testimony whereof I afiix my signature.

LOUIS A. HAZELTINE. 

